The present invention relates to a water-soluble film or sheet, and more particularly to a water-soluble film or sheet of a special polyoxyalkylene compound.
Hitherto. films of polyvinyl alcohol (hereinafter referred to as "PVA"), methyl cellulose, polyethylene oxide, starch and hydroxypropyl cellulose are known as water-soluble films, and PVA sheets are also known as water-soluble sheets. In particular, water-soluble PVA films and sheets are widely employed at the present time. The water-soluble PVA films have been employed. for instance, as unit packaging films of various materials such as germicide, insecticide and dyestuff, laundry bags for hospital use or the like, backing films for wall papers with adhesives, and wrapping films for a sanitary napkin. Also, the water-soluble PVA films and sheets have been employed, for instance, as water-soluble tapes. The water-soluble PVA films and sheets are colorless, transparent, excellent in physical properties such as tear strength and insoluble in most of organic solvents, and have an adequate moisture absorbing property and an oil resistance.
It is known that polyethylene oxide having a high molecular weight provides a water-soluble film. However, polyethylene oxide having a film-forming property must have a very high molecular weight, e.g. more than 200,000, and such a polyethylene oxide is expensive as compared with PVA.
Hithereto, polyoxyalkylene high molecular weight compounds having an average molecular weight of not less than 20,000 have been prepared by, for instance, as represented by polyethylene oxide, polymerizing an alkylene oxide such as ethylene oxide in the presence of a special catalyst such as diethylzinc, strontium carbonate or triethyaluminum under a special polymerization condition (e.g. in a solvent such as n-hexane, 1.4-dioxane or n-heptane). However, in such a conventional process, the solvent is indispensable for promoting the polymerization, and a step for removing the solvent such as distillation is required for taking out the product after the completion of the polymerization. Also, since a metal ion such as Zn.sup.2+ or Al.sup.3+ of the metal compound used as a catalyst remains in the so obtained product. it causes a problem upon using the product in various purposes such as a binder for granular agricultural chemicals and a binder for use in inorganic industry.
On the other hand, it is known to prepare water-soluble high molecular weight compounds (polyester resins) by esterifying a relatively low molecular weight polyalkylene glycol used as a glycol component with a dicarboxylic acid such as maleic acid or succinic acid or its derivative. However, in this process, it is necessary to control the content of the polyalkylene glycol low for producing the high molecular weight compounds. For this reason, the product has been merely employed in limited purposes e.g. modification of polyester fibers.
It is an object of the present invention to provide novel polyoxyalkylene high molecular weight compounds which are soluble in organic solvents and/or water, moldable, and usable in many purposes.
A further object of the invention is to provide a process for preparing polyoxyalkylene high molecular weight compounds which are soluble in organic solvents and/or water moldable and usable in many purposes.
Another object of the invention is to provide a novel, inexpensive water-soluble film or sheet of a polyoxyalkylene compound having physical properties comparable or superior to those of a water-soluble PVA film or sheet and being also soluble in organic solvents.
These and other objects of the present invention will become apparent from the description hereinafter.